The present invention relates to a television signal receiver method and device for receiving and processing television signals (RF) that comprises modulated video signals and modulated audio signals, the receiver comprising a tuner for input of selected television signals and output of at least intermediate frequency (IF) signals; filters; and demodulators for obtaining audio signals and video signals for further processing, e.g. for display of a picture with sound corresponding with the television signals. The known television signal receivers are described hereafter in more detail.
Generally, two types of processing are known for processing the IF signals from the tuner. These methods are known in the art as intercarrier SIF processing and QSS SIF processing. SIF stands for Sound IF, more specifically the FM modulated sound subcarrier signal. QSS stands for quasi split sound.
As will be described below in intercarrier SIF processing, the IF signal from the tuner is subjected to a video and sound SAW filter, followed by a demodulator, which also outputs SIF signals. The SIF signals comprise modulated audio signals on a carrier frequency, which is equal to the difference between a carrier frequency of the modulated video signals and a carrier frequency of the modulated audio signals in the original television signal. An audio demodulator subsequently demodulates the SIF signals to obtain demodulated audio signals.
Although this known art is relatively economical as a result of the low degree of complexity, the sound sensitivity in such a known system is poor. Further, when the demodulator for demodulating the IF signal subjected to the video and sound SAW filter, is accompanied by an IF amplifier, intermodulation occurs, thereby lowering the quality of at least the sound accompanying a picture, or even the picture itself, when displaying images corresponding with the television signals. This intermodulation in the IF amplifier, accompanying the demodulator, results from the difference between the carrier frequency for the audio signals and the color carrier frequency for the video signals, which difference frequency depends on the television signal standard adopted for the television signals concerned.
According to QSS SIF processing, the IF signal from the tuner is, in parallel, subjected to both a video SAW filter with audio attenuation and an audio SAW filter with video attenuation, each followed by a demodulator for video and audio, respectively. In such a QSS SIF configuration a quality of both video and audio can be maintained at a high standard, but only at considerable costs, as an additional SAW filter, amplifier and demodulator for audio IF signals are required.
Notwithstanding the high costs associated with the QSS SIF processing, implementation thereof is desirable, not only because of the poor sound sensitivity and/or even picture deterioration associated with intercarrier SIF processing, but also because increasingly cable networks are taken into operation, which cable networks do not follow established cable standards. In such cable networks, which do not follow established standards, the intermodulation disturbance associated with the intercarrier SIF concept, which results in intermodulation of the carriers of video, more especially chrominance, signals and audio signals leads to a considerable deterioration in the sound quality or even the picture quality.
It is therefore an object of the present invention to provide a television signal receiver, in which the above stated disadvantages are overcome or at least diminished, to which end a television signal receiver according to claim 1 is provided. Advantageous embodiments are defined in the dependent claims.
In a television signal receiver according to the present invention well filtered and amplified SIF audio signals can be obtained, to be demodulated thereafter, where these SIF audio signals are of a quality, which is comparable with that of the conventional QSS SIF processing, while the high costs associated with this conventional QSS SIF processing are avoided, as no additional audio SAW filter for IF signals is required. Simultaneously the audio quality and even the picture quality can be enhanced in relation to the conventional intercarrier SIF processing, while also an adequate solution is provided for cable networks, which do not follow established standards.
Preferably the television signal receiver according to the present invention is such, that the tuner and the generator form a unit. In such a way the tuner/generator provides not only the IF signal, but simultaneously also the SIF signals, whereby a further simplified configuration can be obtained. Nonetheless, the generator and the tuner can be separate components.
Further preferred embodiments are defined in the dependent claims, including optional configurations for the generator.
These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.